Health and Social Care Secretary Jeremy Hunt has described this winter as the "worst ever" for the NHS, as the latest figures show January's accident and emergency waiting time targets had the second lowest result on record.
The Health and Social Care Secretary said the flu outbreak had been "very, very tough" on frontline services, adding: "In terms of pressures on the system, I think it probably is the worst ever because we've got very high levels of demand."
In an interview with ITV News, he refused to apologise to under pressure NHS staff, adding: "When they signed up to go into medicine, they knew there would be pressurised moments."
But Mr Hunt did say sorry to patients, telling the programme: "I take responsibility for everything that happens in the NHS. I apologise to patients when we haven't delivered the care that we should."
He was speaking as figures released by NHS England show that just 85.3% of patients were seen at accident-and-emergency departments within the waiting-time target of four hours in January.
NHS England said the "worst flu season in years" had put a strain on services, but the result was an improvement on December and January last year - the joint worst months since records began.
More than 1,000 patients had to wait more than 12 hours to be seen - more than double the previous month, described as "shocking" by Royal College of Nursing chief executive Janet Davies.
"There's no more graphic illustration of how tough this winter has been for NHS patients and staff than the fact that last month, over 81,000 people going to A&E had to wait more than four hours for a bed in the hospital - the worst figure on record," she added.
"Over a thousand of those had to wait a shocking 12 hours or more."
She said "distressing scenes of frail elderly people in corridors on trolleys have become an all too familiar sight this winter", which is pushing people to quit the NHS.
Dr Nick Scriven, president of the Society for Acute Medicine, said the figures demonstrate how the NHS does "not currently have a sustainable model" to cope during the busy winter months when illnesses such as flu and norovoris are more prevalent.
Figures also released by Public Health England (PHE) on Thursday show there have been 215 confirmed flu-related deaths so far this winter. PHE said flu levels remain high but are continuing to stabilise across the UK.
"The last six weeks has seen the acute services of the NHS under a sustained period of stress due to 'normal' winter pressures along with a surge in influenza," Dr Scriven added.
"Last year we coined the phrase 'eternal winter', but the last month and a half has shown an even steeper decline in performance as demonstrated by all the data available - particularly around ambulance delays, the four-hour emergency target and bed occupancy both in acute beds and critical care."
NHS England said more than 1.7 million patients were seen within four hours last month, an increase of 5.72% on the daily average for the same month last year.
Labour's shadow health secretary Jonathan Ashworth said: "This January was the worst month on record for major A&Es, with over 1,000 patients being stuck on trolleys for over 12 hours and a staggering 515% increase in those waiting over 4 hours compared with January 2011.
"The appalling human stories arising from the worst winter crisis on record have shocked the nation."
An NHS England spokesman said: "Despite the worst flu season in seven years, A&E performance improved this month.
"It was better than both the month before, and was better too than the same time last winter.
"This was partly helped by the fact that NHS-related delayed transfers of care fell to their lowest in four years freeing up beds for patients needing emergency hospitalisation."